Purification of detergent compositions



United States Patent C) PURIFICATION OF DETERGENT COD [POSITIONS VincentA. Sullivan, Jr., Lyon, and Zdzislaw Joseph Ptasinski, Chicago, 11].,assignors, by mesne assignments, to The Stepan Chemical Company,Chicago, 111., a corporation of Delaware No Drawing. Filed June '30,1954, Ser. No. 440,544

14 Claims. (Cl. 252-161) Our invention relates to novel and uniquesynthetic detergent compositions and an improved method for theirpreparation, and more particularly, to improved compositions of the typecharacterized by the presence therein of water-soluble anionicsulfonated detergents in the liquid state, and the method of preparingthe same.

As is well known, the ever increasing need for improved liquid detergentcompositions has resulted in the expenditure of a substantial amount ofresearch time and attention. The particularly complicated physical andchemical phenomena here involved have, however, added a great deal ofconfusion to the art and have given rise to a great plurality ofconflicting theories and concepts. The complexity of the overall problemis readily appreciated when one considers the fact that the phenomenahere involved include suspension, interfacial tension, micellarstructure, dispersion, emulsion, foam stability and the like.

As is pointed out in United States Patent No. 2,607,740, issued August19, 1952, to Peter T. Vitale and Ralph Spencer Leonard, and assigned toColgate-Palmolive-Peet Company, recently synthetic detergents of a typeknown as organic sulfonates have been developed, and the detergents ofthis characteristic type have been found to have certain propertieswhich render them much more suitable than ordinary soaps for certainuses. Since these detergen-ts have many properties substantiallydifferent from the properties of soaps, and particularly, since theybehave in a substantially different manner in aqueous solution, forexample, by the non-formation of insoluble precipitates in hard water,the improvement or alteration of the general behavior characteristics ofthese detergents has opened up an entirely new field of research. One ofsuch fields of research involves certain attempts to prepare thesedetergents substantially free from impurities, and particularlyinorganic salt impurities. The presence of such salts often adverselyafiects such properties as the cloud point (in liquid compositions) andalso has an adverse effect upon the overall cleansing properties. It ishighly desirable to have detergent compositions of this particular typewhich possess excellent clarity in combination with excellent detersiveefficiency; and this particular combination of properties is of veryappreciable import-ance in connection with consumer appeal for home use,as well as for industrial use.

Although detergents of this type can be, and are currently being,packaged and sold in dry particular form, the presence of such saltimpurities therein tends to create additional precipitate depositsduring use. Also, certain features of this type of packaging leavesomething to be desired; and there has developed a very great demand onthe part of home users as well as industrial users for suitablesynthetic detergent compositions in liquid form. Those skilled in theart, however, recognize fully that a rather substantial number ofcritical considerations are involved in the formulation of a suitableliquid detergent composition, and certain of the more important of theseparticular considerations are set forth at some length in said U.S.Patent No. 2,607,740, and need not be elaborated upon at this point inthis disclosure. The main point here involved is that a commerciallysuitable composition must necessarily have suitable properties inconnection with the critical considerations such as viscosity, selectivesolvent, cloud point, foaming, grease emulsification, soil removal,adequate concentration and lack of irritants in the composition. Ingeneral, the liquid detergent compositions heretofore known have leftsomething to be desired in connection with one or more of the foregoingcritical consideration, because of the presence therein of the saltimpurities just mentioned.

The purification problem here involved may best be analyzed by a carefulstudy of the procedure employed for preparing such detergents. Ingeneral, the first step involves sulfonat-ion of a suitable compoundsuch as dodecyl benzene to yield a crude mixture of dodecyl benzenesulfonic acid and the sulfonating agent. Any suitable sulfonating agentmay be used, and those most commonly employed are concentrated sulfuricacid (H chlorosulfonic acid (ClSO H) and sulfur trioxide (S0 Theequations involved may be represented as follows:

1 mol 1.1 mol +H2SO4 H30 C 12H25- C1211: S 0 3H +C1SO3H H01 C123: CmHa S0311 The product shown in each case is a true sulfonic acid having a CSOH group and this is the predominant product obtained using vigorousanhydrous reaction conditions. Actually, at least some sulfate (i.e.COSO H) is usually formed also. The conditions involve minimum reactiontemperatures (i.e. not above IOU-110 F. if possible) to avoiddiscoloration and a substantial excess of the sulfonating agent toinsure substantially complete sulfonation of the hydrocarbon (which isby comparison relatively expensive).

The next step involves washing of the crude sulfona-ted product withwater to remove the excess sulfonating agent (which is effectivelyconverted into H 80 by the Washing process) so as to remove the bulk ofthe excess in the form of a concentrated (80%) solution of H 80 In orderto avoid excessive loss of the sulfonated hydrocarbon (and to obtain aconcentrated H 80 solution) only a relatively small amount of water isused. The dodecyl benzene sulfonic acid, however, has a selectiveretention or absorption with respect to the sulfuric acid and it isimpossible to remove all of the sulfuric acid from the sulfonic acid bythis washing. The resulting washed crude sulfonic acid product has acomposition of about 88% dodecyl benzene sulfonic acid, 7% sulfuricacid, 4% water and 1% dodecyl benzene. Prior to our work in this field,no practical method had been devised for removing a greater proportionof the sulfuric acid.

The next step involves neutralization of the washed crude sulfonic acid;and this may be done by the use of inorganic bases such as alkali metalor ammonium hydrox-ide or by the use of organic bases such as theethanolamides. Here again, low temperature of not more than about -110F. is used to avoid discoloration. If, for example, sodium hydroxide isused, the resulting neutralized sodium dodecyl benzene sulfonatecontains about 12% Na SO (As used herein the terms and parts meanspercent and parts by weight, unless otherwise designated). Otherinorganic bases cause the formation of the corresponding amounts oftheir sulfate salts. It will thus seen that the presence of suchinorganic sulfate salts in the final neutralized sulfonated product isinherent and unavoidable.

As those skilled in the art will readily appreciate, the rathersubstantial amount of the inorganic salt impurity in such compositionsgreatly impairs their use as chemical intermediates for other reactionsand also as ingredients suitable for admixture with other ingredients toform detergent compositions, for example. Moreover, the inorganicsulfate impurity has solubility characteristics that are substantiallydifierent from those of the organic sulfonate .and the use of selectivesolvents in liquid detergent compositions containing these sulfonateddetergents is further complicated. It will also be appreciated that thesulfonated detergent per se is generally looked upon as the sulfonicacid, or the sulfonic acid anion properly speaking, but it is necessaryas a practical matter to neutralize the sulfonic acid to form the saltthereof for use in detergent compositions. As has been pointed out,however, there was heretofore no known practical method of separatingthe sulfate anion (neutralized or unneutralized) from the sulfonate; andthe inherent presence of these substantial amounts of sulfate anion isnot'at all desirable.

If an organic base, suchas triethanolamine, is used to neutralize thecrude washed sulfonated detergent then triethanolamine sulfateimpurities are formed. Such organic sulfate impurities are not asradically different from the'solubility characteristics of the sulfonateas are the inorganic sulfates. For this reason, the inorganic baseneutralized sulfonated detergents have been replaced by thoseneutralized by organic bases in many uses. The organic base neutralizedsulfonated detergents also leave much to be desired, however, sincetheir use may involve the use of a sulfate having better solubility butnevertheless a sulfate which introduces undesirable sulfate anions intothe system. Also, the organic bases such as the alkylolamines arerelatively expensive and the alkylol amine employed in neutralizing thesulfuric acid is for all intents and purposes lost or Wasted as far asdetersive efficiency is concerned.

It is, therefore, an important object of our invention to provide animproved method of producing low-sulfate content anionic sulfonateddetergents, and the improved detergents resulting therefrom.

It is a further object of our invention to provide an improved method oftreating a composition comprising essentially 100 parts of water-solublesalt of anionic sulfonated detergent having a long aliphatic chain of 8to 22 carbon atoms that has been neutralized only to a pH of 66.5 andcontains 1 to 20 parts of inorganic sulfate salt whereby the amount ofinorganic sulfate salt therein may be reduced to a predetermined amountx, within the range of 0.4 to 0.8 part, which comprises intimatelyadmixing the composition with /2 to 5 times its weight of a one phasesolvent system of water admixed with low molecular weight solvents ofthe class consisting of alcohols, ketones, esters and others in anamount sufiicient to reduce the total solubility of the system for theinorganic sulfate salt to x, then maintaining the admixture at 130-140F. for a time sufiicient to completely dissolve the sulfonated detergentand to effectively crystallize the undissolved inorganic sulfate saltparticles therein, and then filtering the admixture to remove thecrystallized salt particles therein.

It is another object of our invention to provide an improved filter aidfor use in the aboveindicated process for producing a substantially(inorganic) salt-free detergent.

Other objects, features and advantages will become apparent to thoseskilled in the art from the following detailed disclosure of preferredembodiments of our invention.

A basic aspect of our invention consists in a method of treating acomposition comprising essentially watersoluble alkaryl anionicsulfonated detergent having a long aliphatic chain of 8 to 22 carbonatoms having residual sulfonating agents therein that comprises firstneutraliz ing only to a pH of 6-6.5 and then intimately admixing thecomposition with substantially an equal weight of ethanol and water involume ratio of 50:50 to 60:40, heating the admixture to from F. toboiling temperature for a time suflicient to completely dissolve thesulfonated detergent and to effectively crystallize the undissolvedinorganic sulfate salt particles therein, and then filtering theadmixture to remove the crystallized salt particles therein.

The anionic sulfonated detergents which we may employ in the practice ofour invention area well known class of compounds, as is pointed out insaid Patent No. 2,607,740. These detergents are all made by procedurescomparable to that hereinbefore described The sulfonation may take placeusing a variety of suitable source materials each having an aliphaticchain of about 8 to about 22. The sulfonation may take place with higherfatty alcohols, so as to obtain, for example, lauryl sulfonate andpreferably C -C alkyl sulfonates. Most preferably, however, alkylarylcompounds are used. The aromatic or alkylaryl sulfonate detergents arewell known in the art. They may be mononuclear or polynuclear instructure. More particularly the aromatic nucleus may be derived frombenzene, toluene, xylene, phenol, cresols, naphthalene, etc. The alkylsubstituent on the aromatic nucleus may vary widely, as long as thedesired detergent power of the active ingredient is preserved. While thenumber of sulfonic acid'groups present on the nucleus may vary it isusual to have one such group present in order to preserve as much aspossible a balance between the hydrophilic and hydrophobic portions ofthe molecule. a

More specific examples of suitable alkyl aromatic sulfonate detergentsare the higher alkyl aromatic sulfonates. The higher alkyl substituenton the aromatic nucleus may be branched or straight-chain in structure;it comprises moreover such groups as decyl, dodecyl, keryl, pentadecyl,hexadecyl, mixed long-chain alkyls derived from long-chain fattymaterials, cracked parafiin wax olefins, polymers of lower monoolefins,etc. Preferred examples of this class are the higher alkyl mononucleararyl sulfonates wherein the alkyl group is about 8 to about 22, andpreferably about 12 to 18 carbon atoms. More particularly, it ispreferred to use the higher alkyl benzene sulfonates wherein the higheralkyl group is about 12 to 16 carbon atoms. For'example, propylene maybe polymerized to the tetramer and condensed with benzene in thepresence of a Friedel-Crafts catalyst to yield essentially the dodecylbenzene derivative which is suitable for sulfonation to the desiredsulfonate compounds.

The above mentioned anionic detergents are used or ultimately obtainedin the instant invention in the form of their water-soluble salts, whichsalts include the ammonium, alkali metal and alkaline earth metal salts,ob tained by neutralization with an inorganic base, and the alkylolamine salts normally obtained by neutralization with the correspondingorganic base. Such salts include the lower three alkali metals (lithium,sodium and potassium, which are the only commercially significant alkalimetal salts), the lowest alkaline earthmetal-magnesium (which is themost significant of this class) the ammonium salts, and the triethanolamine salts. Although in certain instances, the alkylol amine salts havebeen found to be particularly preferable (e.g., the monoethanolamine,diethanolamine, triethanolaminesalts and mixtures thereofhave been foundto be particularly useful); however, we have alsofound that the alkalimetal salts, particularly the alkali metal alkyl benzene sulfonates areadvantageous in many respects including economic aspects and arepreferred for use in the instant invention. The problem here solved isthat of obtaining these sulfonate salts in a substantially sulfate-freecondition.

As also explained, the procedure for the preparation of the sulfonateddetergent inherently results in the incorporation therein of the sulfate(anion); and subsequent neutralization merely results in the formationof the corresponding sulfate salt as an impurity. No practical methodwas heretofore known for avoiding the presence of the neutralized orunneutralized sulfate in such sulfonated detergent compositions.

The details of the sulfonation process per se are old and well known tothose skilled in the art, and need not be discussed at length herein.The formation of a sulfonated anionic detergent is, likewise, a wellknown procedure. A suitable sulfonatable detergent source material(having a long aliphatic chain of about C -C which may be a hydrocarbon(e.g. dodecyl benzene), an alcohol (e.g. lauroyl diglyceride), etc., isreacted with one of the sulfonating agents hereinbefore described. Mostpreferably the source material is a C -C alkyl benzene, and the claimsherein are addressed primarily to the purification of the alkaryldetergent.

The result of the sulfonating reaction is a member of the well knownclass of detergents called anionic sulfonated detergents; and suchsulfonated compounds by virtue of their retentive powers for thesulfonating agent inherently contain substantial quantities of the same,even after washing or any other known refining treatment. After washing,these sulfonated detergents inherently contain from about 3% to about ofthe sulfonating agent, depending to some extent upon the particularagent. (Using sulfur trioxide it is possible to obtain a lower percentretained than by using sulfuric acid.) Neutralization of the washedsulfonated product results in a neutralized product which may containfrom about 5% to about 20% of the neutralized sulfonating agent as thesulfate salt of the neutralizing base. Again, the neutralizedsulfate-containing product is well known in the art. Our inventioncontemplates departing from the well known complete neutralization stepto the extent that neutralization is carried only to a pH of 6-6.5 toobtain the neutralized product as a starting material, when such isneutralized with an inorganic base; and this material is here defined asa composition comprising essentially water-soluble alkaryl anionicsulfonated detergent salt having a long aliphatic chain of 8 to 22carbon atoms having a pH of 6-6.5 and containing 5 to 20 weight percentthereof of inorganic sulfate salt. The invention also contemplates theuse of certain specific filter aid compositions which have been found tohe usually superior in performance.

The nature of our invention may probably best be demonstrated bycarrying out a specific process embodying the invention, as follows:

A starting material is provided which has the following approximateformulation:

88% dodecyl benzene sulfonic acid, 7% sulfuric acid,

4% water, and

1% dodecyl benzene.

This material is obtained by sulfonating a suitable alkyl aromaticcompound (viz. dodecyl benzene) with any of the aforementionedsulfonating agents (specifically, chlorosulfonic acid) in slight excess,followed by washing with about an equal volume of water to remove thebulk of excess sulfonating agent. Next, the material is neutralized byan inorganic base (i.e. sodium hydroxide) using an amount sufiicient toraise the pH only to about 6-6.5. This results in the presence of only aslight trace of free acid in the composition.

The composition thus comprises essentially watersoluble alkaryl anionicsulfonated detergent salt having a long aliphatic chain of 8 to 22carbon atoms, having a pH of 6-6.5 and containing 1 to 20 weight percentthereof of an inorganic sulfate salt, and more specifically, sodiumdodecyl benzene sulfonate containing 12% sodium sulfate (whosepreparation was described in detail hereinbefore). The composition wasadmixed with an equal weight (and, preferably, /2-1 /2 times thecomposition weight) of 55 volumes of ethanol and 45 volumes of water,which effectively reduces the sulfate concentration to 6% in theadmixture. This ethanol-water solvent (system) is capable of fullydissolving the sulfonate detergent, but it is capable of actuallydissolving only about 0.3% sulfate maximum, which means that 5.7%sulfate is excluded from the solvent phase and a two-phase systeminvolving a second dispersed sulfate phase is formed. Ethanol:watervolume ratios of 60:40 to 50:50 may be used to obtain admixtures whichdissolve about 02-04% sulfate.

As will be appreciated, the neutralization to pH 6-6.5 with sodiumhydroxide was carried out at temperatures not in excess of -l10 F. andthe subsequent solvent addition has served to cool the admixturesubstantially below the neutralization temperatures. Under suchconditions the second dispersed sulfate phase is barely apparent, if atall, since we have found that the dispersed sulfate particles areextremely minute in character. In fact, it might be expected that thepresence of the sulfonate in solution would create a selective solventsystem for all of the sulfate; instead, we believe that the sulfonatecontributes materially to the almost infinitely fine dispersion hereobtained but does not actually retain the sulfate in solution (in excessof the 0.3

There is no known way of separating this fine sulfate dispersed phasefrom the solvent phase so as to obtain a one-phase (solvent-phase)system. As such, the dispersed sulfate cannot be filtered out or removedby any other known practical means. We use the term dispersed sulfate todescribe the undis'solved sulfate advisedly because we have found thatthe sulfate is, in fact, not soluble in this system and must, therefore,be undissolved and dispersed therein. Others may not have appreciatedthis fact, and considered the sulfate to be dissolved, but with orwithout the knowledge that the sulfate cannot be dissolved in truesolution there is still no apparent method of removing the (undissolved)sulfate.

A key to the sulfate removal, we have found, is, first, carryingneutralization only to pH 66.5 and, secondly, heating instead ofadditional cooling (normally permitted to take place). For example, theabove described admixture was heated to F. and maintained thereat forone-half hour, and it was found that noticeable precipitation and/ordispersion crystallization had taken place in connection with thesulfate particles. The removal of these crystallized particles byfiltration, at the heated temperature, using a standard grade filtercloth or screen, plus standard filter aids in a filter press is thenaccomplished and the filtered product has a sodium sulfate content of0.3% (in the one-phase solvent system).

As mentioned, one important feature here involved is the neutral'mationonly to pH 6-6.5. Neutralization to a lesser extent could be used (onlyto 5 or 5.5 pH, for example) but no improvement in results will beobtained and the amount of free acid remaining is appreciably greater soas to create a corrosion problem and to result in the (formation of anappreciable amount of inorganic salt during a subsequent neutralizationcompletely to pH 7. With neutralization to pH 6-6.5 the free acidremains only in trace amounts; and subsequent neutralization to pH 7does not result in the formation of an appreciable amount of inorganicsalt. Neutralization beyond about pH 6.5 appears not to be helpfulbecause the reduction in the trace amounts of free acid isinconsequential; and filtration is made more ditficult.

Although it is not desired to limit the invention to any particulartheory, we believe that the unusual result here obtained may -beexplained as follows:

The addition of the ethanol-water solvent to the sulfonatehaving'dissolved therein the sulfate creates a system wherein only asmall part of the sulfate is soluble and the remainder of the sulfateproceeds to precipitate or separate from the solvent phase. Theinitially precipitated or separated particles are almost colloidal insize but under ordinary conditions would build up into crystals ofappreciable size. The sulfonate in this systern, however, prevents thisbuild-up perhaps by forming a protective film on the surface of theseparticles as soon as they take form. The result is what appears to be atrue solution but which has a relatively high cloud point. In ourinvention, however, we heat this system for the purpose of increasingthe solubilizing activity of the solvent phase presumably so that thisprotective film may be removed or otherwise rendered ineffective andcoagulation of the minute particles may take place to form a filterableprecipitate. It is also understood that sol-gel systems are responsiveto the pH, there being a tendency, for example, for silica sol solutionsto remain stable at pH 7 but to gel at a pH above or below. Here thelower pH (which mi-ght even be caused by addition of another acidaftercomplete neutralization) may well contribute to the coagulation orgelling of the colloidal-size particles, or it may merely interfere withthe dispersing function of the detergent and/or assist the aqueousalcohol in removing the protective detergent In any event, the operatingtemperatures and times are both reduced materially by the use of thelower pH (e.g. pH 6-6.5). In the solvent system here employed, theproportions of the solvents used are determined by two considerations,the amount of sulfate to be retained in solution and the ultimatesolvent proportions desired in the filtered one-phase system which, inturn, is governed by the subsequent use contemplated. For example, if adry powdered detergent were to' be made, then any reasonably volatilesolvent might be used. If a concentrated liquid detergent were to bemade, then those solvents to be used as the selective solvent (in theproportions desired) should be used, if possible.

Certain considerations are quite important, however;

first of all, the solvent must contain at least some and preferablyabout 20 volume percent water. If all ethanol is used, it is found thateffective crystallization (upon heating) cannot be obtained. Again, thereason for this is not fully understood, but apparently the solventsystem requires some water to act upon the sulfonate which is believedto prevent effective crystallization. In addition, the presence of waterin the solvent system prevents the undesirable colloidal precipitationof the inorganic salt. Most preferably an ethanol-water'mixture is used,since ethanol is the ideal organic solvent for liquid I detergents,having no characteristic odor or other features which might limit itsuse in such compositions.

Also, the most effective coagulation results are obtained using theethanol-water system. In general, the ethanol: water volume ratio shouldbe 50:50 to :40, and most preferably it is 55 :45 which effectivelyresults in a reduction of the sulfate to about 0.3% as described.Actually, the ethanohwater volume ratio. may be adjusted through therange of, for example 3:5 to 4:1 to suit particular circumstances. At a4:1 ratio a minimum amount of sulfate (i.e. about 0.1%) is retained insolution; and at 3:5 ratio proportions of sulfate in the range l%-5% maybe obtained so as to bring the sulfate concentration-at least below'thatordinarily possible during careful washing and neutralization. Atethanol:water ratios-of less than 1:1 (or 50:50), however, thecoagulationrate is slower. In general, the 60:40 to 50:50 eth-anolzwaterrange is preferred and this results in (after admixture with an equalweight of crude sulfonated detergent) about a 0.2 to 0.8% sulfatecontent.

Lower concentrations of sulfate in a given one-phase system may beobtained, for example, by the use of 4:1 ethanolzwater with an equalweight of crude sulfonate, so as to obtain a 50% sulfonate solutioncontaining about 0.1% sulfate and then diluting the solution with equalits weight of otherdetersive orthe like agents and/or solvents so as toobtain as little as 0.05% of the sulfate. A sulfatezsulfonate weightratio of about 1:500 is about the minimum, however; and sulfateconcentrations in the range ODS-0.2% must usually be obtained by alsodiluting the sulfonate concentration to as low as 25%. The result is watone-phase system of lower suifonate concentration that is capable ofdissolving only ODS-0.2% sulfate.

Although we have emphasized the use of ethanol in our process, as thepreferred organic solvent, it should be understood that" our inventionalso contemplates the use of other organic solvents. Such solventsinclude particularly the water-miscible alcohols (e.g. methanol andpropanol), ketones (e.g. acetone), esters (e.g. methyl formate), andetbers (e.g. dimethyl ether). As will be appreciated, the water-miscibleorganic solvents are capable of forming a one-phase solvent system withwater, and each of the inorganic sulfates (e.g. Li, Na, K, NH Mg, etc.sulfates) is substantially insoluble in these organic solvents.Accordingly, if it is desired to obtain a solution containing x amountof sulfate (within the range of, for example, 0.4-0.8part per parts ofsulfonate), one selects a predetermined water-solvent system foradmixture with the sulfonate so that the resulting one-phase.(sulfonate-containing system) will have a total sulfate solubilityof'0.4-0.8 part. 'In so selecting the system to be used, the amount tobe used may also be considered since'the crude sulfonate may be admixedwith from about /2 to about 5 times its weight of solvent if desired(although about equal the weight is preferred in making concentratedliquid detergents).

It will also be'understood that the instant invention does not precludethe use of water-immiscible solvents, but these solvents must be used ina system in which they are miscible, if a one-phase system is to beobtained. Thus, if it is desired to use butanol which is only about 9%soluble in water, it would be necessary to use a water: propanokbutanolsystem of perhaps 70:15:15 volume ratio in order to obtain a one-phasesystem. a

It will thus be seen that the selection of the solvent system to be usedmay be made from a variety of comj pounds and proportions, in the lightof the present teachings, so as to obtain a number of differentpredetermined results.

After the sulfonated detergent has been neutralized to a pH 66.5 by aninorganic base (which might be a carbonate or other basic compoundinstead of the hydroxide) and the inorganic salt of the sulfonateddetergent containing the residual inorganic sulfate has been admixedwith the selected solvent system, at the neutralization temperature orbelow, it will be noted that no appreciable coagulation can be observed.The next step, however, involves the effective crystallization of theundissolved (undissolvable) sulfate; and this step involves just theopposite to what would normally be done at this time. Up to this pointin the procedure the'avoidance of heating the composition is veryimportant; and, as a general rule, it was assumed that heating above theminimum temperature maintainable during neutralization should never becarried out.

We have found, however, that just the opposite is true. After theneutralization is completed, so that no harm ful effects (possiblybecause of sulfuric acid present) can be obtained by heating, then weadd the solvent system a ing filtration so as to have maximum sulfateiaesgeae of heat); but the second step of crystallizing the sulfateparticles is substantially slower. In its initial aspects cloudinessappears (and this would ordinarily be a signal to anyone to avoidheating); but particles of suitable size to be filtered develop uponstill further heating. The development of particles of fiiterable sizewill, of course, be ascertainable to an operator from testing samples ofthe batch. In general, at least about one-half hour of heating isrequired for heating at the preferred temperatures of 120-150 F. (themost preferred being 130-140 F.). In general, also the mixture must beheated to at least about 115 F. to get an effective crystallization rateand heating above about the boiling temperature at least so as toproduce conditions more vigorous than moderate reflux is usually notdesirable. Atmospheric pressure is suitable, of course. As mentioned,the effective completion of the crystallization step is readilyascertainable by routine examination and testing.

Next, the mixture is filtered. Any type of filtration generally suitablefor removing solids from a solvent system of this type may be used(although a distinctly superior filter aid has been found and Will bedescribed). Filter systems of the type used to purify lacquer solutions,liquid a filter cloth employing a precoat.

An important aspect of the filtration step is the maintenance of heat inthe admixture. In other Words, the mixture is filtered hot, preferablyat the temperature of crystallization and at least prior to anyappreciable coolling thereof. Complete cooling of the mixture to downbelow the neutralization temperature, for example, tends to impairappreciably the efiectiveness of the filtration process. Most preferablythe mixture is filtered at at least the minimum effectivecrystallization temperature (i.e. about 115 F.). This has an additionaladvantage that maximum crystallization is, in fact, maintaineddurparticle removal.

Actual tests of the final product indicate that this product is, infact, a one-phase system having dissolved therein the sulfonate and avery minor amount of residual sulfate. The solvent system above iscapable of dissolving as much sulfate as is finally retained in thesystem; and accordingly, the only sulfate in the system is in solution.

As hereinbefore explained, the organic solvents here used are capable ofdissolving substantially no inorganic sulfate salt, so the amount oforganic solvent used in the solvent system is selected as the principalfactor governing final sulfate-concentration. At least some water isused, presumably to cooperate with the organic solvent and the sulfonateto efiect coagulation, and this amount of water is ordinarily sufficientto make possible the presence of at least dissolved sulfate, in minor ortrace amounts.

An important additional aspect of the invention resides in the discoveryof a uniquely superior filter aid. A vast number of filter aids areknown and used commercially. Most of these include essentially inorganicnon-fibrous materials such as filter clays; but the general particle 7sizes, characteristics, etc. of all of these materials effectivelyclassify the same under the genus filter aids on the basis of theirknown function of collecting (before or during) filtration on the filterscreen or cloth and thereby affording a filter bed impervious to thematerial being filtered out but readily penetrated by the filtrate. Wehave found that ordinary filter aids assist in the removal of thesulfates if the conditions hereinbefore described are used; or if(neutralization is not stopped at 66.5 pH and) the instant compositionin the presence of the solvent solution is heated at least to 135 F.(preferably to 175 195 F. and most preferably to 185 F.) untilcrystallization takes place. If neither procedure is followed, however,ordinary filter aids are not sufficiently effective. We have found afilter aid composition which is, however, effective if heating iscarried out only to about 115 F. or more; and this composition is evenmore effective (than any other filter aid) if either of the aboveprocedures is also carried out.

The filter aid which we have found to be unusually effective is onecomprising at least 5% vegetable fiber filter aid and particularly,cellulose fiber filter aid. The remainder can be any commercial gradefilter aid-vegetable or mineral-fibrous or non-fibrous. Cellulose fiberfilter aids actually have very short fiber sizes, in the nature of ballmilled cellulose fibers used as synthetic resin fillers. The surfacearea of cellulose fibers is, however, immense. The fibers are understoodto comprise elongated interwoven fibrils about 1.4 microns thick; thefibrils are bundles of ultrafibrils which are 0.1-0.3 micron thick; theultrafibrils are, in turn, composed of micells also assumed to beinterwoven long slender threads; and the micells may be pictured asropes comprising 150 cellulose molecular chains arranged as a crystallattice. The micells are understood to have a diameter of about 60-70Angstrom units and a length of at least 600 Angstrom units. The spacebetween the cellulose molecular chains is very small, sometimes as smallas 10-15 Angstrom units. Apparently, the dispersed sulfate particle sizeremains small enough to pass through this fine lattice of molecularchains when neutralization is first carried out and it is not untilheating at at least about F. for a little while that these particlescoagulate to the extent necessary to be trapped in this fiber latticeduring filtration. If the heating is carried out at at least about F. orif neutralization is carriedonly to pH 66.5 (with heating to at least115 F.), then the filtration process is greatly facilitatedand thecellulose fiber filter aid is clearly helpful (although absolutelyessential to satisfactory commercial operation).

Most satisfactory filtration is obtained using notmore than about 25%cellulose fiber filter aid, about 10% being most preferred. Theremaining filter aid preferably contains an equal amount of fibrousinorganic material, such as asbestos or chrysolite, amphibole fibers,etc.

Typical formulations are as follows:

Formulation I For each 80 parts of material to be filtered:

cellulose fiber Formulation II For each 80 parts of material to befiltered:

1 part of powdered cellulose fibers, 5 parts of diatomaceous earth, and1 part of clay filter aid.

The cellulose fibers are thus about 525% and the remainder is preferablyinorganic filter aids, with about 525% fibrous inorganic filter aids.

Still another aspect of the instant invention resides in an improvedmethod for producing certain organic base neutralized sulfonateddetergents. As will be appreciated, the organic base sulfate salts aresoluble in the organic solvents (such as ethanol) here employed and suchsulfate may not be eliminated as the inorganic sulfates may. The organicbases are usually the amine bases and the most common of these are thealkylolamines (i.e. C -C alkanol amines having not more than one OHgroup on a C atom), including monoalkylol, dialkylol, trialkylol, etc.amines, specific examples of which include monoethanol, diethanol,triethanol, monopropanol, etc. amines. At present, the most satisfactorycommercially available alkylaryl sulfonates are the triethanolaminesalts, which about-0.3% ammonium sulfate dissolved therein.

-zaraconsidered superior to various other organicas welleasinorganicbase neutralized sulfonates of this class. 130116 otithereasonsfor thisv allegedsuperiority is based..upon.the-;supe1iorsolubility of triethanolamine sulfate,.as:comparedio-the inorganic sulfates. However, thepres- ,ence ofthetriethanolamine sulfate is stillnot desirable; it is merely lessundesirable.

. lnsour invention we use-:as. a neutralizingagentfor the sulfonateddetergent-an ammonium basesuchasammoniaor ammoniumv hydroxide so .as toobtain a com- ..position consisting essentiallywof ammonium salt of thesulfonated detergent,- :as. for example, bysubstituting am- -monia for,the sodium .hydroxideused in. the demonstration .hereinbefore describedso: .as toobtain. a; composition of ammonium-.dodecyl: benzenes-ulfonate-containingabout 10%ammoniumsulfate. (The ammonium cation has.less-molecular weight than the :sodium cation). .We .-may then use.anequalweightof anhydrous ethyl alcohol andcarry: out the.mixing,'heating and filtering .as..describediso as to obtain acne-phasesystem containing To .precipitate the ammonium; saltsubstantially,anhydrous .alcohol ..(alkanol) must be.aused,.and preferably, anhydrousethanol.

. Next, we.=add. to this system. a small amount of tri- .ethanolamine(soas to insure maintenance oi an alkaline spI-Iaduringthe subsequent.reaction) and we react the :ammonium dodecyl benzenesulfonateithereinwith a suitab1e.,C C alkylene oxide such ,as ethyleneor propylene 1oxide. .The ..-ethylene oxide combinesat a ratio of 3 molsto-oneot the sulfonate so as :to form triethanolamine v dodecylbenzenesulfonate. The reaction of ethylene oxide with an. ammonium salt iswell: known and need {not bedetailed herein. The ingredients arepreferably enclosedin a vessel and the ethylene oxide is added theretowith agitation under a slight pressure of 10 pounds .per square inch(gauge) and at temperatures of 100-200" F, Otherknown amine additionreactions may .be employed to obtain other amine salts of the detergent.

' Comparable results-to those obtainedusing a sodiumhase-.neutralization-, may .also be obtained using other unetal .bases,suchasthe .lithium magnesium or potassium bases. Likewise, comparableresults'may be obtained using other sulfonated detergents ,such asthe C-C alkyl aryl hydrocarbons such as decyl benzene, lauryl benzene, keryl'benzene,tetradecyl benzene, myn'styl benzene and: .hexadecyl Ibenzenesulfonates.

Alterations and modifications may be made in the formulations hereinwithout departing. from the scope of the present invention.

'We claim as our invention:

1. A method of producing a substantially inorganic salt-free detergentfrom, alcomposition consisting essentially of. a water-soluble alkarylanionic sulfonated detergent salt having a long aliphatic chain of 8 to22 carbon atoms containing llto 20 weight'percentthereof of an alkalimetal sulfate-salt and havinga pH of just less than 7, which methodcomprises intimately admixing the composition withsubstantially.an-equal:weight of ethanol andwater. in .volume ratio of 50:50 to60:40, m'aintaining'the admixtureat 1207150? F fora time sufii-...cient,to completely dissolve. thesulfonated detergent, and

V to. effectively crystallize theundissolvedsulfate-salt particlestherein, and then separating the crystallizedsalt particles .from thedissolved .detergentand-neutralizing V 'thedetergent to. at least pH 7.

' 1,2. A methodot producing a substantiallyinorganic salt-free detergent.froma composition consisting essentially of 100 parts .ofawateresoluble alkarylanionic sulfonated detergent .salt .havingalongaaliphatic chain of 8. to 22 carbon -atoms,.-ha ving a. pH-f 6.6.5and con- .taining 1.10.20 :parts ofaninorganic sulfate salt, of theclass consisting of alkali metal and. alkaline earth;metalsulfates,..whercby. .themamount oftjinorganicsulfate salt(thereintrnayj-berreduced to a predetermined amount,-

.withinthe range of 10.4 to 0.8 part, which. method cornprisesintimately admixingthe composition with, /z. to

5 .times .its-weight.v ofa one-phase solvent ,systemtot wateraadmixedwith low molecular weight solvents of the class consisting of .alcohols,ketones, .esters .and ethers in an amount suflicient to reducethetotal.solubility of the system for the inorganic sulfatexsaltto .saidpredetermined amount, then maintaining the admixture at 120- .3 carbonatoms.

4. The method of claim 2 wherein the detergent is a salt of higher alkylmononuclear arylrsulfonate detergent,

.said higher alkyl; group having. 8 to 22' carbon. atoms.

5. The method of 'claim 3 wherein the alkanol :is

7 ethanol.

6. The method of claim 4 wherein the detergent and the inorganic saltare both salts of an alkali metal.

7. The method of claim, 5'wherein' the detergent :is Y sodiumdodecylbenzene sulfonate and the inorganic sulfate salt is sodiumsulfate.

8. A method -.of reducing, the sodium sulfate content to 0.20.4 weight,percent of. acomposition having. a pH of 6,-6.5; andconsisting'rssentially .of sodium..dodecylbenzene sulfonate detergent.and 53130 15*WGight-PQICEIHZ thereof of sodium sulfate, whichmethodcomprises, ad-

mixing the composition with substantially equal its weight of ethanoland water 'in volume ratio of :45, holding the admixture at 135 F. forat least about /z hourto completely dissolve the detergent and toefiectively; cry- .tallize the undissolved: sodium sulfate and thenfiltering ,the admixture to removefthe ,undissolved sodium sulfate.

9. A:method,of,reducingithe sodium sulfate content to 0.2-0.4 weightpercent of a composition .havinga pH of 6-6.5 and, consisting.essentiallyof sodium .dodecylbenzene sulfonatedetergent and 5 tol5i'weight percent :thereof of .sodium, sulfate,.swhich method comprisesadmixing the composition with substantially to 1% times its weight ofethanol. and waterrin volume ratio of 55:45, holding thel-admixtureyat115 R; to the boiling point for. at least about /2hourtoxcompletely"dissolve the detergent and :toxefliectivelycrystallize the .undissolved sodium sulfate andthen filtering theadmixture'through a filter aid.of 95'-75 minerals and 5-25 veg'etablefibers to remove thexundissolved sodiumsulfate.

10. A method of preparing a substantially inorganic salt-free detergent,that comprises sulfonating dodecylbenzene by reaction" therewith of asuitable excessof a sulfonating agent of the class consistingof-concentrated sulfuric acid, chlorosulfonic -acid and sulphurtrio'xide, undersubstantially anhydrous conditions, then-washing thereaction product to =obtain-a composition consisting essentially ofdodecylbenzene sulfonicacid and residual sulfonating agent, neutralizingthe composition to a pH of just lessthan pH 7' withaa sodium base-to--'obtaina composition consisting essentiallyof sodiumdodec'ylbenzene sulfonateand sodium sulfate salt'=inresidual amounts andadmixing the neutralized composition-with substantially an equal weightof ethanol andwater 'in volume ratio of 50:50 to 60:40, maintainingthe-admixture at -15 0 F. for a time suifieient to completely dissolvethe sulfonated detergent and to" effectively crystallize the undissolvedsodium sulfate salt particles therein, then separating thecrystallizedsalt -particles*- from the mixture and finally neutralizingto at -least pH 7. p

11. Amethod of preparing asubstantially-inorganic salt-free detergent,that comprises sulfonating-"dodecylbenzene. by reaction therewith ofasuitable excess -of a sulfonating agent and .thenwashingsthecreactionproduct to obtaina composition consistingtessentially of dodecylbenzenesulfonic acid and residual sulfonating agent, neutralizing thecomposition to a pH of 6-6.5 with an ammonium base to obtain acomposition consisting essentially of a dodecylbenzene sulfonate salt ofthe base containing residual amounts of a sulfate salt of the base,

then intimately admixing the composition with substau-' tially an equalweight of anhydrous ethanol, maintaining the admixture at 120-150 F. fora time suflicient to completely dissolve the sulfonated detergent and toelfectively crystallize the undissolved inorganic sulfate salt particlestherein, and then filtering the admixture to remove the crystallizedsalt particles therein,

12. A method of preparing a substantially inorganic salt-free detergent,that comprises sulfonating alkylbenzene having 10 to 14 carbon atoms inthe alkyl group by reaction therewith of a suitable excess of asulfonating agent of the class consisting of concentrated sulfuric acid,chlorosulfonic acid and sulphur trioxide, under substantially anhydrousconditions, and then washing the reaction product to obtain acomposition consisting essentially of the alkylbenzene sulfonic acid andresidual sulfonating agent, neutralizing the composition to a pH of 66.5with an alkali metal base to obtain a composition consisting essentiallyof the alkylbenzene sulfonate salt of the base containing residualamounts of a sulfate salt of the base, then intimately admixing thecomposition with substantially an equal Weight of ethanol and water involume ratio of 50:50 to 60:40, heating the admixture to from 115 F. toboiling temperature for a time suflicient to completely dissolve thesulfonated detergent and to effectively crystallize the undissolvedinorganic sulfate salt particles therein, and then filtering theadmixture through a filter aid comprising at least vegetable fiberfilter aid and the remainder mineral filter aid to remove thecrystallized salt particles therein.

13. A method of preparing a substantially sulfate-free triethanolaminedodecyl benzene sulfonate, that comprises sulfonating dodecyl benzene byreaction therewith of a suitable excess of a sulfonating agent and thenwashing the product to obtain a composition consisting essentially ofdodecylbenzene sulfonic acid and residual sulfonating agent,neutralizing the composition to a pH of 6-6.5 with an ammonium base toobtain a composition consisting essentially of ammonium dodecylbenzenesulfonate and ammonium sulfate in residual amounts, then admixing theneutralized composition with substantially an equal weight of anhydrousethanol, maintaining the admixture at 115 F. to boiling temperature fora time suflicient to completely dissolve the sulfonate and toeffectively crystallize the undissolved sulfate, filtering to removesuch crystallized undissolved sulfate, and then treating the filteredcomposition with ethylene oxide to convert the ammonium sulfonate totriethanolamine sulfonate.

14. A method of preparing a substantially inorganic salt-free detergent,that comprises sulfonating an alkylbenzene having 10 to 14 carbon atomsin the alkyl group by reaction therewith of a suitable excess of asulfonating agent of the class consisting of concentrated sulfuric acid,chlorosulfonic acid and sulphur trioxide, under substantially anhydrousconditions, and then washing the reaction product to obtain acomposition consisting essentially of the alkylbenzene sulfonic acid andresidual sulfonating agent, neutralizing the composition to a pH of 66.5with an alkali metal base to obtain a composition consisting essentiallyof the alk'ylbenzene sultonate salt of the base containing residualamounts of a sulfate salt of the base, then intimately admixing thecomposition with substantially an equal weight of ethanol and water involume ratio of :50 to :40, heating the admixture to from F. to boilingtemperature for a time sufficient to completely dissolve the sulfonateddetergent and to effectively crystallize the undissolved inorganicsulfate salt particles therein, and then filtering the admixture toremove the crystallized salt particles therein.

References Cited in the file of this patent UNITED STATES PATENTS2,283,199 Flett May 19, 1942 2,316,719 Russell Apr. 13, 1943 2,463,497Smith Mar. 1, 1949 2,467,130 Hunt Apr. 12, 1949 2,567,854 Nixon Sept.11, 1951 2,678,906 Kohn May 18, 1954 2,687,420 Brady Aug. 24, 1954 OTHERREFERENCES Seidell: Solubilities of Organic and Inorganic Compounds,vol. 1, 1919, page 671.

1. A METHOD OF PRODUCING A SUBSTANTIALLY INORGANIC SALT-FREE DETERGENTFROM A COMPOSITION CONSISTING ESSENTIALLY OF A WATER-SOLUBLE ALKARYLANIOMIC SULFONATED DETERGENT SALT HAVING A LONG ALIPHATIC CHAIN OF 8 TO22 CARBON ATOMS CONTAINING 1 TO 20 WEIGHT PERCENT THEREOF OF AN ALKALIMETAL SULFATE SALT AND HAVING A PH OF JUST LESS THAN 7, WHICH METHODCOMPRISES INTIMATELY ADMIXING THE COMPOSITION WITH SUBSTANTIALLY ANEQUAL WEIGHT OF ETHANOL AND WATER IN VOLUME RATIO OF 50:50 TO 60:40,MAINTAINING THE ADMIXTURE AT 120-150*F. FOR A TIME SUFFICIENT TOCOMPLETELY DISSOLVE THE SULFONATED DETERGENT AND TO EFFECTIVELYCRYSTALLIZE THE UNDISSOLVED SULFATE SALT PARTICLES THEREIN, AND THENSEPARATING THE CRYSTALLIZED SALT PARTICLES FROM THE DISSOLVED DETERGENTAND NEUTRALIZING THE DETERGENT TO AT LEAST PH 7.